1. Field of the Invention
The present invention relates, in general, to an apparatus for conditioning polishing pads and, more particularly, to an apparatus for conditioning the polishing pads of a chemical-mechanical polishing system.
2. Description of the Prior Art
In a process of producing semiconductor devices, such as CMOS, an etchback process or chemical-mechanical polishing process has been typically used for flattening the surfaces of wafers to a desired level. Of the above-mentioned two processes, the chemical-mechanical polishing process (hereinbelow, referred to simply as xe2x80x9cCMP processxe2x80x9d) has been more preferably used since it more precisely flattens the surfaces of wafers and gives desired flatness to the wafers.
The CMP process performs a mechanical polishing using a polishing pad and a chemical polishing using polishing slurry at the same time. During such a CMP process, the polishing pad is gradually and partially abraded as time goes by, so the pad fails to desirably polish the surface of a wafer or accomplish desired flatness of the wafer""s surface. In such a case, it is almost impossible to accomplish almost impossible to accomplish intrawafer regional flatness or interwafer flatness, which are the final aim of the CMP process.
It is thus necessary to rework such partially abraded polishing pads, and the reworking of the polishing pads is so-called xe2x80x9cconditioningxe2x80x9d in the field, and has been typically performed by a pad conditioner.
FIGS. 1a and 1b are views showing a conventional disc-type diamond conditioner and a method of conditioning a polishing pad using the diamond conditioner.
As shown in FIG. 1a, the conventional disc-type diamond conditioner 10 comprises a disc body 2 made of stainless steel, with diamonds 6 having a diameter of several ten micrometers and fixed to the lower surface of the disc body 2 using a nickel or chrome plating layer 4. The diamond conditioner 10 is placed on a polishing pad 14 seated on a rotary surface table 12, and is rotated by a drive unit 16, thus grinding the surface of the polishing pad 14 to a desired depth by the diamonds 6. The polishing pad 14 is thus reworked such that it has a desired flatness.
Such a conditioning process must be periodically performed during a CMP process such that the surface of a polishing pad maintains a desired flatness of not higher than 2 xcexcm.
However, the conventional conditioning process using such a diamond conditioner is problematic in that it has a low conditioning efficiency due to frictional point contact of the diamonds with the surface of the polishing pad and uneven cutting angles of the diamonds. In order to overcome such a problem, the diamond conditioner is pressed onto the surface of the polishing pad under high pressure. However, the polishing pad is typically made of a synthetic polyurethane material, and so the conditioning process may be not smoothly performed when the conditioner even slightly excessively compresses the polishing pad. It is also almost impossible to give a desired flatness of not higher than 2 xcexcm to the surface of the polishing pad.
In addition, the nickel or chrome plating layer 4 fixing the diamonds 6 to the lower surface of the conditioner 10 is also ground during the pad conditioning process, and so the diamonds 6 may be popped-out from the conditioner 10 and undesirably driven into the polishing pad 14.
The diamonds, driven into the polishing pad, scratch the wafer""s surface during a CMP process, thus reducing the quality of wafers. Therefore, such polishing pads, into which diamonds are driven, must be replaced with new pads, and the conditioner from which diamonds are popped-out must be replaced with a new one. This increases the processing cost of a CMP process, including a pad conditioning process.
Therefore, it is necessary to provide an apparatus and method of conditioning such polishing pads, which gives a desired flatness to the pads without allowing the pads to form scratches on the surfaces of wafers due to popping-out of diamonds during a CMP process.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus for conditioning the polishing pads of a CMP system, which positions a tool having a cutting tip at a side of a polishing pad such that the cutting tip is aligned with a target depth of cut in the pad, and which moves the tool on the pad in a radial direction of the pad at a constant velocity while rotating the pad, thus conditioning the pad.
In order to accomplish the above objects, the present invention provides an apparatus for conditioning the polishing pads of a CMP system, comprising: a tool having a cutting tip and positioned almost perpendicular to the surface of a polishing pad arranged on the rotary surface table of the system, a horizontal moving unit for moving the tool in a direction almost parallel to the surface of the polishing pad, a base unit positioned at a side of the rotary surface table and supporting the horizontal moving unit, and a vertical moving unit for adjusting a vertical position of the tool relative to the surface of the polishing pad.
The apparatus of this invention preferably further comprises an inclination control unit for adjusting an angle of inclination of the horizontal moving unit relative to the surface of the polishing pad, thus allowing the tool to move horizontally in a direction precisely parallel to the pad""s surface.
In the preferred embodiment of this invention, the horizontal moving unit comprises a horizontal slide arm holding the tool at a first end thereof, a horizontal casing connected to a second end of the horizontal slide arm and having a guide rail for guiding a horizontal movement of the slide arm relative to the horizontal casing, and a drive unit for moving the slide arm along the guide rail of the horizontal casing. In such a case, the vertical moving unit preferably comprises a first level screw provided at the first end of the horizontal slide arm for adjusting the vertical position of the tool relative to the surface of the polishing pad.
In the preferred embodiment, the inclination control unit comprises a second level screw provided at the base unit for moving one end of the horizontal casing in a vertical direction, and a hinge joint connecting a predetermined portion of the horizontal casing to the base unit and adjusting the angle of inclination of the horizontal casing relative to the surface of the polishing pad in response to an operation of the second level screw.
In the present invention, a diamond tip is preferably used as the cutting tip of the tool.
Different from a conventional conditioning apparatus flattening the surface of a polishing pad through a grinding process with surface to surface contact between the pad and a disc-type diamond conditioner, the conditioning apparatus of this invention conditions the surface of a polishing pad by moving a tool with a cutting tip on the pad""s surface while rotating the pad after positioning the tool on the pad""s surface such that the cutting tip is aligned with a target depth of cut in the pad.
That is, during a rotation of the polishing pad on the rotary surface table of the CMP system, the tool having the cutting tip is horizontally moved on the pad""s surface in a direction from the edge to the center or from the center to the edge, thus uniformly flattening the entire surface of the polishing pad while overcoming the problem of the conventional disc-type diamond conditioner causing inferior flatness of the pad""s surface due to both uneven distribution of vertical pressures and a difference in rotating force between the inside and outside portions of the diamond conditioner.
In the apparatus [and method] of the present invention, a tool having a cutting tip is used during a conditioning process. This tool gives a desired flatness to the polishing pads without allowing the pads to form scratches on the surfaces of wafers due to popping-out of diamonds during a CMP process, different from a conventional disc-type diamond conditioner.